Venous Laser Updates: New Wavelength or New Fibers?

Introduction

Since the introduction of endovenous lasers (EVL) in the early 2000s, procedure methodologies, as well as device technologies, have evolved extensively in the endeavor to improve treatment outcomes. As each novel parameter has been studied, new data have enabled the venous ablation community to acquire an enhanced understanding of the laser’s mechanism of action. The primary subject matter in EVL studies has routinely included one or a combination of the following: laser fiber vein-wall contact,^1,2 linear endovenous energy density (LEED),  ^3,4 laser power settings,⁵ variable laser wavelengths,^6,7 and most recently, covered laser fibers.^8,9 This article aims to provide a succinct review of these major topics, from EVL inception to the latest methodologies employed by thought leaders.

Evolution of EVL Technology

The shift from pulsed energy to continuous laser energy. Initial investigators of endovenous lasers employed methodologies that involved laser fiber vein-wall contact and bare-tip fibers to deliver pulsed energy. Users combined manual compression with a slow pullback of the fiber.^1,2,10 At this early juncture, it was believed that the primary mechanism of action for vein obliteration was direct contact with the vessel wall.¹⁵ The pulsed method with applied compression produced several perforations at the site of contact of the bare-tip fiber with the vessel wall, resulting in high rates of post-operative pain and bruising.^1,2,10–12 Ensuing these early adverse findings, investigators began utilizing continuous energy instead of pulsed energy, and discontinued the use of manual compression.^2,10 Other early researchers postulated that laser-induced steam bubble formation, similar to direct fiber-tip contact, caused perforations of adjacent wall areas.^11,12 Proebstle¹³ and Perkowski¹⁴ both proposed that the primary mechanism of action for 940 nm EVL was the formation of steam bubbles via delivery of laser energy, causing thermal injury to the vein endothelium, resulting in thrombotic occlusion. This mechanism was further defined by Proebstle et al¹⁸ using in vitro generation of steam bubbles with 810, 940 and 980-nm lasers. Each laser was examined in saline, plasma and hemolytic blood.¹⁸ None of the lasers were able to produce steam bubbles in saline or plasma alone, but did create perforations at sites of direct laser-tip contact.¹⁸ However, all lasers did produce steam bubbles in hemolytic blood, indicating that hemoglobin plays a key role in inflicting thermal damage to the vein wall.¹⁸ Original data from these studies helped to form the opinion that vein-wall perforations and extravasation of blood into surrounding tissues are the culprits in causing EVL post-operative pain and bruising.⁸ Procedurally, it is now largely accepted that the use of manual compression to achieve direct laser fiber-tip contact actually exacerbates the incidence of perforation and extravasation, and hence the incidence of pain and bruising. Linear endovenous energy density (LEED). Subsequent to the steam-bubble mechanism of action premise, several researchers began to evaluate LEED for its effect on treatment outcomes. LEED is best defined as the number of joules delivered per centimeter of the target vein during an EVL procedure.¹⁷ Efficacy has been the primary endpoint of LEED studies, evaluating low LEED versus high LEED. In initial studies, Timperman et al^3,4 determined that energy doses > 80 J/cm produced more efficacious results than LEED 60 J/cm.¹⁶ Pannier et al²¹ evaluated a 1470 nm laser, reporting a 100% success rate with an average LEED of 107 J/cm for great saphenous vein treatment. It was noted that in the limbs which received a LEED > 100 J/cm, there was a considerably higher incidence of paresthesia (15.5%) than limbs receiving 21 The data from these studies suggest that the optimal LEED is in the range of 60 J/cm to 100 J/cm.^3,4,16,21 LEED in these studies below the target range led to failure, whereas, high LEED demonstrated increased side effects.^3,4,16,21

Effect of Varying Laser Power on Outcomes

Similarly, power (watts) has also been assessed for its influence on EVL treatment results. Proebstle et al¹⁷ selected patients with clinical stage C2 or higher to receive treatment with a 940 nm laser using either 15 W or 30 W. The study revealed that the 15 W group with an average LEED of 18.4 J/cm had 11 treatment failures within the first 3 months, whereas, the 30 W group with an average LEED of 68.4 J/cm did not have any treatment failures in this timeframe.¹⁷ There were no tangible differences noted between the 15 W group and 30 W group in terms of side effects.¹⁷ However, the rates of pain (72–82%) and ecchymosis (78–82%) were extremely high for both groups, suggesting that both 30 W and 15 W may be high enough power settings to cause an increase in side effects. In an analogous study, a 1470 nm laser was evaluated at both 15 W and 25 W settings.⁵ The average LEED for both power groups was between 109.7 J/cm and 132.6 J/cm, yielding a 100% occlusion rate for each.⁵ While there were no statistically significant differences in side effects, the investigators observed a lower instance of pain, bruising, and reduced use of analgesic tablets in the 15 W group.⁵ Although the utilization of higher power settings to achieve the target LEED produces a high rate of treatment success, the data suggest that a higher wattage leads to increased post-operative pain and bruising. When planning treatment, the clinician should consider this data when choosing power settings and target LEED.

Effect of Varying Wavelengths on Outcomes

One of the currently most debated questions in EVL ablation is: Does wavelength make a difference? At the outset of laser technology, 810, 940, 980, and 1064 nm wavelengths each were touted to be the most optimal wavelength for steam-bubble formation and, hence, thermal damage to the vein. As the market has evolved, 1,320- and 1470 nm wavelength lasers have been introduced, generating a new theory about how higher wavelength lasers work. Some thought leaders have coined the terms hemoglobin-specific laser wavelengths (HSLWs) and water-specific laser wavelengths (WSLWs) to differentiate between wavelength mechanisms of action.^19,25 Water-specific lasers are hypothesized to produce intimal damage by targeting the interstitial water in the vein wall, utilizing water as a chromophore to absorb laser energy.^20,25 In addition, leading engineers are testing the theory that the light generated by WSLWs is absorbed by the fluid in red blood cells, but at the time of this publication, there were no published data on this concept. Only the 1,320- and 1470 nm wavelengths are believed to produce thermal damage in this fashion; the higher the wavelength, the greater the affinity for water absorption.^5–7 As discussed earlier, hemoglobin-specific lasers are conjectured to produce thermal damage through utilizing intravascular blood as a chromophore to absorb laser energy and create steam bubbles.^11,19 810, 940, 980, and 1064 nm lasers are considered to have an inclination for hemoglobin absorption, with the lowest wavelength having the highest specificity for hemoglobin.^8,20 The concept of variable specificity of hemoglobin and water based on wavelength has prompted several head-to-head wavelength studies in recent years. One of the first studies on wavelength difference was published in 2006, comparing an 810 nm laser to a 980 nm laser.⁶ At equivalent LEED, there were no dissimilarities in treatment success between the groups at any point of procedural follow up.⁶ Reported side effects did differ, with the 980-nm cohort showing considerably less bruising (p 7 The wavelengths did not demonstrate any differences in efficacy; however, the 1320-nm group reported significantly lower pain (p 7 A significant factor in this study is the difference in wattage between the 1320 nm wavelength and the 940 nm wavelength at 30 W. Using 8 W of power, the 1320 nm group yielded an average LEED of 62 J/cm; similarly, the 940 nm group produced a LEED of 63 J/cm by utilizing a power of 30 W.⁷ The higher WSLWs are able to produce high LEEDs using significantly less power than the lower-wavelength HSLWs. This raises the question of whether the lower noted side effects with the 1320 nm laser are a result of water specificity or due to the low power utilized. Mackay et al¹⁹ conducted a pilot study that evaluated an 810 nm laser with a 1320 nm laser, treating only patients with bilateral venous insufficiency so that both lasers could be used on each patient. The same treatment parameters of 8 W of power and a target LEED of 80 J/cm were employed for both laser groups.¹⁹ At 3–4 days post procedure, the 810 nm laser reported an average pain level of 2.3 and the 1320 nm laser reported average pain of 0.9 on a scale of 0–5.¹⁹ During the same post-operative visit, bruising was graded on a scale of 0–5, with the 810 nm treated limb scoring a 1.7 and the 1320 nm limb recording a 0.9.¹⁹ Statistical analysis was not performed for these data; nonetheless, the 1320 nm treated limbs reported significantly less pain and bruising than the 810 nm limbs, suggesting that with all parameters equal, the higher 1320 nm wavelength was the contributing factor to less side effects. Several conclusions can be drawn from these data, in particular, that all wavelengths are efficacious in the eradication of veins when delivered at the optimal LEED and power. Furthermore, the lower the wavelength, the greater the hemoglobin affinity; hence, a higher number of vessel perforations and a higher probability of short-term side effects. In addition, the specificity for water absorption demonstrated by the 1320 and 1470 nm wavelengths implies that their interaction with endothelial cells in the vein wall may be similar to the collagen shrinkage mechanism observed during radiofrequency (RF) procedures. This offers an explanation for the low rate of pain and bruising observed with both RF and WSLW technologies. Another explanation for the performance of 1320 nm and 1470 nm wavelengths are their ability to use lower power to produce high target LEED, as evidenced by Proebstle’s data.⁷ These data imply that water-specific lasers may produce a more efficient energy absorption. Lastly, although higher wavelengths have exhibited less vein perforations and less pain and bruising, inadvertent contact of a bare-tip fiber with the vein wall cannot be prevented with any certainty. While the newer wavelengths have improved treatment outcomes, the primary side effects of ecchymosis and pain still remain at the forefront as the shortcomings of EVL with bare-tip fibers. Table 1 provides a summary of wavelength characteristics, as well as the results of wavelength head-to-head studies, comparing the data that were provided in each of the studies. For the pain and bruising scores, some investigators reported the average score (0–5), whereas others only reported the total percentage of patients who experienced pain or bruising.

Covered Fibers

Jacket-tip laser fibers. The newest endovenous laser technology revolves around fiber-tip interaction with the vein wall. This innovative technology features a “jacket-tip” design, which employs either a metallic²² or a ceramic²³ cover at the distal tip of a laser fiber. A jacket-tip fiber (Figure 1) utilizes one of these coverings to envelop the energy-emitting portion of the fiber. The jacket functions to prevent the flat emitting face of a bare-tip fiber (Figure 2) from coming in contact with the vessel wall. As several studies have established, perforations created from the bare tip of the fiber rendering contact with the vein wall are the principal cause of post-operative pain and bruising.^1,2,8,10,12 Therefore, the prevention of inadvertent fiber-tip contact should eliminate perforations that would otherwise be caused by direct contact. This hypothesis was tested in a randomized study which evaluated bare-tip laser fibers versus jacket-tip laser fibers using a 980 nm laser.^24,26 Forty-five male and female patients who were on a waiting list for great saphenous vein treatment were selected in succession and informed of their randomization into either the bare-tip or jacket-tip fiber group.²⁶ The procedure entailed continuous pullback of the laser fiber and sheath through the vein segment at a target standard energy rate of 100 J/cm at 12 W.²⁶ A duplex ultrasound was performed at 72 hours post procedure to assess efficacy, which was reported as 100% for both treatment groups.^24,26 Patients were required to record a pain score for each of the first 7 days using a 10-point analogue scale.²⁶ At 7 days post procedure, patients were also graded on ecchymosis using a scale of 0–5 by a nurse who was blinded to fiber use.²⁶ Significant differences were noted for each of these endpoints, most notably the patient-reported pain scores, which averaged 1.87 for the bare-tip group opposed to 0.96 for the jacket-tip group (p 26 (Table 2). With all other variables being equal, the jacket-tip fiber demonstrated the ability to prevent perforation and extravasation, thereby yielding considerably lower pain and bruising scores than the bare-tip fiber. However, only the pain score was statistically significant. These results reveal that use of a jacket-tip laser fiber produces a low incidence of short-term side effects and a more tolerable post-operative recovery. Although the average J/cm for the jacket-tip group (82.3 J/cm) was lower than the bare-tip group (86.2 J/cm), this difference was not statistically significant, and hence had no effect on treatment outcomes. The prevention of vein-wall contact and perforation by the jacket tip are the plausible contributing factors to the differences in side effects.

Metallic-tip laser fibers. Analysis of the only currently available metallic-tip fiber also proposes specific factors that are inherent to the metallic jacket type. The metallic tip, different from the ceramic tip, is secured onto a 600 µm fiber using a weld which causes a divergence of the fiber light.²⁷ This divergence creates a 15º angle on each edge, resulting in an effective fiber diameter of 905 µm.²⁷ The difference in fiber diameter produces 2.2 times lower power density, which translates into 56% less power interaction with intravenous blood and an ability to generate coagulation as opposed to the cutting action observed with bare-tip fibers.²⁷ Less power interaction, in effect, allows the metallic-tip laser fiber to generate high target LEED using significantly less power than would be required for a bare-tip fiber, similar to the efficiencies demonstrated by the water-specific lasers. In addition, the metallic tip provides a 0.010 inch buffer between the emanating portion of the fiber and the vein wall, further reducing any probability of perforation.²⁷ As a final point, EVL ablation with the use of a jacket-tip fiber provides added evidence that there is no need for laser-tip wall contact to ablate the vein.

Summary

In summary, endovenous lasers were conceptualized to improve patient recovery and outcomes in comparison to the widely used vein-stripping method. The efficacy of EVL has been evident from the outset; however, pain and bruising have been points of contention, even as the procedure has progressed. Each advancement that the EVL procedure has undergone has provided compelling data, from LEED and power settings, to variable wavelengths and covered fibers. The newer, water-absorbing 1,320- and 1,470-nm wavelengths have thus far provided dynamic evidence that their mechanism of action specifically targets the vein wall, reducing perforations. Additionally, WSLW use a lower power setting to produce high LEED, demonstrating enhanced efficiency and potentially less perforations. The innovative jacket-tip fiber design essentially provides the “missing piece” of the EVL evolution, in that by covering the emitting face of the bare fiber, it eliminates the possibility of inadvertent fiber-tip contact with the vein. The future of improved EVL treatment outcomes will not be attributed to the laser wavelength, but to the type of laser fiber employed.

References

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From New York University Vein Center, New York, New York.

Disclosure: The author discloses that he is a consultatnt to AngioDynamics.

Address for correspondence: New York University Vein Center, 530 1st Avenue, Suite 6D, New York, NY 10016. E-mail: Lowell.Kabnick@nyumc.org

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VASCULAR DISEASE MANAGEMENT 2010;7(3):E77–E81